1. Field of the Invention
This invention relates to a novel solar tracking device and system which provides both a high level of accuracy and wide angle target finding capabilities. More particularly, it relates to such a device which may be incorporated into a system which eliminates continuous hunting by the tracking device during operation.
2. Description of the Prior Art
There are a variety of solar tracking devices and systems known in the art. For example, Napoli et al., U.S. Pat. No. 4,041,307, issued Aug. 9, 1977 discloses a quadrant detector employing shadowing, which is especially suited for use with solar photovoltaic arrays. However, the detector there disclosed is not suited for use with focused parabolic solar collectors, because such collectors require a much higher degree of accuracy in tracking the sun than is required in the case of photovoltaic arrays. Certain conditions, such as a partly cloudy sky, which produces a large amount of reflected light impinging on the sensors of such a detector, cause severe reduction in accuracy of the system there disclosed.
Other examples of solar tracking devices employing shadowing are disclosed in the following issued U.S. Pat. Nos.: Trihey, 3,996,917, issued Dec. 14, 1976; Haywood et al., 4,082,947, issued Apr. 4, 1978; Winders, 4,107,521, issued Aug. 15, 1978; Neale, 4,146,785, issued Mar. 27, 1979; Brown et al., 4,151,408, issued Apr. 24, 1979; Smith, 4,179,612, issued Dec. 18, 1979. Another example of such a device is disclosed in Pages, French Patent Publication No. 2,257,067, published Aug. 1, 1975.
All of these tracking devices suffer from one or more of the following problems: inability to find the sun from a wide angle off-target; not sufficiently accurate to allow use of a small heat receiver, such as is desired with a parabolic reflector; oscillation across desired attitude, causing motor wear, gear wear and energy consumption; inability to operate in both bright sun and hazy sun. An approach common to many of these devices is to set sensing circuits connected to the devices to respond only when the sensed light is above a relatively high threshold, either through use of biasing resistors or optical filters. This avoids problems associated with high light levels, but produces poor response when the sun is dim. Setting the sensing circuits to respond to a low level of detected light causes problems in bright sunlight.
The above-mentioned U.S. Pat. No. 4,107,521 also discusses the problem of excessive hunting in solar tracking systems. The approach there disclosed for reducing excessive hunting is to reduce tracking speed of the solar energy device to attempt to eliminate overshoot. However, any tracking system set for a very high level of sensitivity will continually hunt back and forth across the target in an arc of greater or lesser size. The reduced tracking speed used in U.S. Pat. No. 4,107,521 will reduce the arc length of the constant overshoot but will not stop the continuous hunting. Further, the approach employed in this patent will not prevent motor jitter and buzz during windy conditions, when optics are being vibrated.
A variety of photodectors are known, in addition to those disclosed in the above patents. For example, NASA Tech Briefs, Vol. 7, No. 1, Fall 1982, p. 78 discloses a photodetector especially adapted for use in a joystick controller.
Various aspects of solar reflectors, support structures for such solar reflectors, drive mechanisms for causing such reflectors to track the sun, and heating systems incorporating such solar reflectors are also disclosed in the following issued U.S. Pat. Nos.: Whitaker, 3,234,931, issued Feb. 15, 1966; Carter et al, 3,305,606, issued Feb. 21, 1967; Hoham, 3,394,054, issued July 23, 1968; Hubbard, 3,977,773, issued Aug. 31, 1976; Kume, 4,034,737, issued July 12, 1977; Fletcher et al, 4,044,753, issued Aug. 30, 1977; Bottum et al, 4,044,948, issued Aug. 30, 1977; Gonzales, 4,061,130, issued Dec. 6, 1977; Brokaw, 4,098,264, issued July 4, 1978; Bottum, 4,130,110, issued Dec. 19, 1978; Raser, 4,147,414, issued Apr. 3, 1979; Winninger, 4,158,356, issued June 19, 1979; Monk, 4,161,942, issued July 24, 1979; Hutchison, 4,178,913, issued Dec. 18, 1979.
As exemplified in these prior art patents, tracking solar collectors and heating systems incorporating such solar collectors have been largely experimental. None have achieved mass production for a variety of reasons. In order to achieve mass production, such tracking solar collectors and their heating systems must meet a number of criteria. The system must be large enough to supply an adequate amount of energy. It must be strong and reliable in operation when subjected to high winds. It must be simple in design to facilitate manufacture and installation by relatively unskilled personnel. The parabolic reflector should be of high optical quality, with a true undistorted parabolic surface. The systems exemplified in the above prior art patents have not met these criteria to a sufficient degree for mass production.
In particular, a shortcoming of prior art systems is that they tend not to utilize mechanical balance. Prior art mechanisms typically include offset pivots, with substantial lever lengths, which increase power requirements for positioning the parabolic reflector. Also, prior art supporting and tracking mechanisms require alignment of moving parts to close tolerances if they are to function without binding or requiring the use of relatively large motors for positioning.
Thus while the art of solar tracking devices, solar reflectors incorporating such tracking devices, drive mechanisms for such tracking solar reflectors and solar heating systems incorporating such tracking solar reflectors is a well developed one, a need still remains for further improvements in such systems, in order to meet requirements for mass production.